syzbot is reporting that mmput() from shrinker function has a risk of
deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.

Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
callback") replaced mmput() with mmput_async() in order to avoid sleeping
with spinlock held. But this patch replaces mmput() with mmput_async() in
order not to start __mmput() from shrinker context.

[1] 
https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45

Reported-by: syzbot <syzbot+1068f09c44d151250...@syzkaller.appspotmail.com>
Reported-by: syzbot <syzbot+e5344baa319c9a96e...@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
---
 drivers/android/binder_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 42c672f1584e..cbe6aa77d50d 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -947,7 +947,7 @@ enum lru_status binder_alloc_free_page(struct list_head 
*item,
                trace_binder_unmap_user_end(alloc, index);
        }
        mmap_read_unlock(mm);
-       mmput(mm);
+       mmput_async(mm);
 
        trace_binder_unmap_kernel_start(alloc, index);
 
-- 
2.18.4

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